Bis(8-hydroxyquinolinium) naphthalene-1,5-disulfonate tetrahydrate

The crystal structure of the organic salt features classical hydrogen-bonding interactions involving the 8-hydroxyquinolinium cation, the naphthalene-1,5-disulfonate anion and the two water molecules of crystallization.


Structure description
8-Hydroxyquinoline (8HQ, C 9 H 7 NO, HL), known also as oxine, is a bidentate chelating agent.It forms three species: H 2 L + , HL and L À .8HQ bearing a hetero-nitrogen atom (pKa = 10.8) and the 8-substituted phenol group (pKa = 4.9) is a good organic acid-base adduct conformer and has been reported to form supramolecularly organized compounds with acidic counter parts under formation of multiple hydrogen bonds (Smith et al., 2003).8HQ is used in analytical chemistry for the quantitative determination of metal ions because the resulting complexes are insoluble in water.The aluminium complex (Co ¨lle et al., 2002;Katakura & Koide, 2006) is a common component of organic light-emitting diodes (OLEDs).Substituents on the quinoline ring result in compounds with luminescence properties (Montes et al., 2006).In its photo-induced excited state, 8HQ converts to zwitterionic isomers, in which the hydrogen atom is transferred from oxygen to nitrogen (Bardez et al., 1997).The complexes as well as the heterocycle itself exhibit antiseptic, disinfectant, and pesticidal properties (Phillips et al., 1956) and functions as a transcription inhibitor (Wen et al., 2023).Its solution in alcohol is used in liquid bandages.It once was of interest as an anti-cancer drug (Zhu et al., 2017;Fouda 2017).The roots of the invasive plant Centaurea diffusa release 8HQ, which has a negative effect on plants that have not co-evolved with it (Vivanco et al., 2004).
1,5-Naphthalenedisulfonic acid (H 2 NDS, Armstrong acid, C 10 H 8 O 6 S 2 ) is a white-to-yellowish solid that is soluble in water (1030 g l À 1 ).It is used in the production of dyes, pigments, and other industrial chemicals.It also functions as a chelating and complexing agent, which is used in various applications such as water treatment, analytical chemistry, and mineral processing (Arslan-Alaton et al., 2008).H 2 NDS does not demonstrate a definite biological activity.Complexes derived from H 2 NDS are of interest in supramolecular chemistry due to their ability to form complex hydrogenbonded systems because the sulfonate group can accept up to six hydrogen bonds.
Preparation and structural characterization of organic salts on basis of these two simple compounds is of interest for supramolecular and analytical chemistry (Oh et al., 2020;Chen et al., 2022).In our previous works (Suyunov et al., 2023a,b,c), we reported on H 2 NDS and its salts involving nickel(II) and cadmium(II).In the current work, we report on preparation and molecular and crystal structures of a proton-transfer salt, 2(8HQ The asymmetric unit of the title compound consists of one 8HQ + cation, half of an NDS 2-anion, and two water molecules of crystallization, resulting in a supramolecular associate with a 2:1:4 cation-anion-water composition.The sulfonic acid (SO 3 H) groups of H 2 NDS are deprotonated, with the hydrogen atoms transferred to the nitrogen atom of an 8HQ + cation, and the NDS 2À dianion exhibits inversion symmetry, with the inversion center located at the midpoint of the C11-C11 i [symmetry code: (i) À x, 1 À y, 1 À z] bond in the naphthalene ring system (Fig. 1).A similar salt with composition 2C 9 H 8 NO + •C 10 H 6 O 6 S 2 2-•2H 2 O was previously reported (Jin et al., 2014), the main difference being the presence of only two water molecules and orthorhombic symmetry (space group Pbca) compared to four water molecules and monoclinic symmetry (space group P2 1 /n) for the title salt.In the cation of the title salt, the angle around the protonated N atom [C7-N1-C8 = 122.67 ( 13) � ] is approximately 1 � less than the corresponding angle in the study of the dihydrate [123.5 (3) � ].In the title salt, the anions exhibit two distinct orientations, with the angle between their planes being 33.37 (7) � .The cations are oriented in a single direction, forming angles of 71.66 (8) and 75.80 (9) � with the planes of the anions.The naphthalene ring system exhibits typical bond lengths and angles, with C-C bond lengths ranging from 1.362 (2) to 1.431 (2) A ˚, and C-C-C angles in the range 117.91 (14) to 123.05 (12) � .The hydroxyquinoline and naphthalene fragments are coplanar with r.m.s deviations of 0.0162 (14) A ˚and 0.0112 (13) A ˚.In the crystal, the 8HQ + cation, the NDS 2-anion, and the water molecules are connected via classical O-H� � �O and N-H� � �O hydrogen bonds (Table 1) with graph-set motifs of R 3 4 (10) and R4 4 (13), which link the components into chains extending parallel to [010], as illustrated in Fig. 2. The SO 3 À data reports Table 1 Hydrogen-bond geometry (A ˚, � ).

Figure 2
The formation of O-H� � �O and N-H� � �O hydrogen bonds (dashed red lines) in the crystal structure, leading to R 3 group on one side of the anion participates in the formation of these chains.The symmetry-related second SO 3 À group also participates in hydrogen bonding under the formation of a second infinite chain parallel to [101] connecting with the previous chains via C-H� � �� interactions (where Cg are the centroids of the naphthalene rings, Table 1) and C(�)� � �C, N(�) weak intermolecular contacts [Cg� � �Cg distance = 3.6547 (9) A ˚, slippage 1.248A ˚], forming sheets parallel to (101) (Fig. 3).These sheets are linked through additional weak C-H� � �O interactions into a tri-periodic network structure.Due to steric hindrance of the sulfonate groups, the nearest centroid separation between naphthalene rings is 5.264 (3) A ˚, suggesting no �-� stacking between these moieties.
A search of the Cambridge Structural Database (CSD, version 5.45, updated November 2023; Groom et al., 2016) revealed that the crystal structure of 8HQ alone has been determined eleven times, while thirteen reports are related to molecular complexes, and 71 crystals are organic salts where the nitrogen atom of 8HQ is protonated.In the case of 1,5-NDSA, 225 crystals are organic salts of 1,5-NDSA in the dianionic form, One compound (FIVFOI01; Du et al., 2019) is a complex with 1,5-NDSA in the monoanionic form, and four crystals are molecular complexes (SAHRIG, Singh et al., 2021;SATBEX, Liu et al., 2017;VEGHUN, Cunha et al., 2017;WEZGAN, Xu et al., 2023) with neutral sulfo-acid molecules.

Synthesis and crystallization
The title compound was obtained by the addition of 1,5naphthalenedisulfonate acid (0.288 g, 1 mmol) to a solution of 8-hydroxyquinoline (0.176 g, 2 mmol) in water, in the stoichiometric ratio 1:2.Good-quality single crystals were obtained by slow evaporation after four days (yield: 60%).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2

Special details
Geometry.All esds (except the esd in the dihedral angle between two l.s.planes) are estimated using the full covariance matrix.The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry.An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s.planes.Refinement.Hydrogen atoms attached to the N and O atoms were located from a difference-Fourier map and refined with bond-length restraints of 0.86 (1) Å and 0.82 (1) Å, respectively.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )

Figure 1
Figure 1The structures of the molecular entities in the title salt, showing the atomlabelling scheme and displacement ellipsoids drawn at the 50% probability level.H atoms are shown as spheres of arbitrary radius and hydrogen bonds are shown as dashed lines.[Symmetry code: (i) À x, 1 À y, 1 -z.]

Figure 3
Figure 3 The crystal packing of the title salt in a view along [101].O-H� � �O, N-H� � �O, and C-H� � �O hydrogen bonds are shown as dashed blue lines, and C-H� � �� and �-� interactions as dashed pink lines.

Table 2
Experimental details.